The present invention generally relates to a system and process capable of providing a real time, in-flight advisory of the structural condition of a helicopter's rotor blade(s). In general, rotor blades have a finite operating life, and they can be rendered unserviceable due to damage and fatigue wear. Failure of the blade spar in flight can be catastrophic; therefore, early blade damage detection and/or blade condition information may provide the capability to avoid blade associated flight hazards. Relatedly, the United States Navy (Navy) and the United States Marine Corps (USMC), as well as Original Equipment Manufacturers (OEM), have determined that there is a need to provide an in-flight warning (or an indication) of blade damage when appropriate, and have used inert-gas-charged spars as a means for determining the condition or the structural integrity of the spar. More specifically, fatigue wear of a spar may cause microscopic cracks to develop in the spar, which should cause the gas to leak from the spar, and which, if such leakage becomes significant, may require the replacement of the blade. Moreover, once the spar gas charge has leaked, due to a crack or damage, the remaining safe flight time for a damaged blade is generally insufficient to continue a mission to normal completion. In other words, the remaining mission time could exceed the remaining spar-life-to-failure-time, which may result in an in-flight failure of the blade. Consequently, in the prior art, a means used to detect spar gas leakage and to provide an indication of a possibly cracked or damaged blade was generally comprised of a pressure detector or pressure activated mechanical device capable of providing a low gas charge pressure warning (or other indication).
As an example of such prior art system, the system currently being used by the Navy and the USMC is called the In-flight Blade Inspection System (IBIS). In general, the IBIS utilizes a radioactive, Strontium 90 source, which is located near the blade root (i.e., the end of the blade nearest the rotor hub) in a removable pressure switch indicator module called the IBIS indicator. This radioactive source is manipulated by the pressure switch in relation to the charge pressure and, based on such manipulation and in association with the use of a radioactivity level-monitoring device located in the aircraft, is capable of providing an indication of a low-pressure condition. Furthermore, the use of radioactive sources is not limited to use outside the aircraft. In addition, the radioactivity level-monitoring device (Detector), used with the IBIS, may contain more of the Strontium 90 isotope.
Because of this, each of these devices, i.e., one indicator per blade and one Detector per aircraft, must be handled as radioactive components, which generally affects the costs associated with repairing, replacing, installing and/or maintaining these devices. Furthermore, the disposal and environmental costs associated with radioactive materials are (or can be) substantial. Moreover, the IBIS has several other significant disadvantages: (1) increased personnel hazards associated with the handling of radioactive material; (2) the incurring of additional costs due to special shipment and accounting procedures for radioactive items; (3) increased environmental hazards, especially in the case of flight or ground mishaps; (4) high repair and/or replacement costs; (5) high disposal costs; and (6) exposing personnel to radioactivity during maintenance and test procedures, which may be further exacerbated by requiring personnel to be in close proximity to the radioactive components.
Therefore, a need remains for a low-cost, yet robust, rotor blade monitoring system that can provide an improved in-flight indication of potential rotor blade faults without the use of radioactive isotopes, that is easy-to-use and relatively simple to manufacture and install on military and/or commercial helicopters—as well as on (or with) other platforms (or components) of interest.